1. Field of the Invention
The present invention relates to an imaging lens, which can be suitably mounted in small-sized information terminals, such as mobile phones equipped with cameras or Personal Digital Assistants (PDAs).
2. Description of the Related Art
Recently, with the propagation of personal computers to general homes, a digital still camera (hereinafter referred to as a ‘digital camera’), enabling image information to be input into a personal computer, has been rapidly popularized. Further, with the realization of high-functionality of mobile phones, a mobile phone equipped with a camera, in which a small-size imaging module is mounted, has also been rapidly popularized. In addition, in the case of other small-sized information terminals, such as PDAs, an information terminal equipped with an imaging module has been popularized.
In such an appliance equipped with an imaging function, an imaging device, such as a Charge Coupled Device (CCD) or a Complementary Metal Oxide Semiconductor (CMOS), is used. Recently, the size of this imaging device has been greatly reduced. Owing to the reduction in the size of an imaging device, in an imaging apparatus using an imaging device such as a CCD, the realization of a small size and a light weight are required for both the main body of the imaging apparatus and the lens mounted in the main body. Further, recently, imaging devices having a large number of pixels have been developed to realize high quality, so that high performance, such as high resolution or high contrast, is also required in a lens system.
As described above, for recent imaging devices, small size and high-pixel density have been realized, and thus high resolution and high structural compactness have been required for imaging lenses for digital cameras. Meanwhile, in the prior art, imaging lenses for small-sized information terminals, such as mobile phones equipped with cameras, are mainly required in order to realize low costs and structural compactness, but, recently, there is a tendency for the high-pixel density of imaging devices to be implemented in mobile phones equipped with cameras. For example, megapixel imaging devices having a number of pixels greater than a million pixels are utilized, and thus the necessity for high-performance imaging devices has increased. Due thereto, the development of various types of lenses in which costs, performance and compactness are considered together is required.
In order to meet such a necessity, a method of configuring a lens using, for example, three or four lens elements is considered to realize compactness and low costs, and a method of actively utilizing aspheric lenses is being considered to realize high performance.
Such aspheric lenses are advantageous in that they contribute to the realization of compactness and high performance, but are disadvantageous in that the manufacturing efficiency thereof may be decreased and the costs thereof may be increased.
Further, when aspheric lenses are actively used, there are problems in that the sensitivity of the lenses is increased, so that assembly efficiency is decreased, and thus productivity is deteriorated.